Since the early 1980's, thousands of patients prone to irregular and sometimes life threatening heart rhythms have had miniature heart-monitoring devices, such as defibrillators, pacemakers, and cardioverters, implanted in their bodies. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current, to their hearts. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives.
The typical implantable heart-monitoring device includes a set of electrical leads, which extend from a sealed housing through the veinous system into the inner walls of a heart after implantation. Within the housing are a battery for supplying power, a capacitor for delivering bursts of electric current through the leads to the heart, and heart-monitoring circuitry for monitoring the heart and determining not only when and where to apply the current bursts but also their number and magnitude.
The monitoring circuitry generally includes a microprocessor and a memory that stores a computer program. The computer program, or more generally the signal-processing algorithm, instructs the microprocessor how to interpret electrical signals that naturally occur during expansion and contraction of a heart muscle. The algorithm also instructs the processor what, if any, electrical therapy should be given to correct abnormal heart rhythms.
In general, these algorithms are either too complex or too simple. Complex algorithms require considerable processing time and power to implement. Greater processing time generally lengthens device response time, and greater power requirements generally shorten the lifespan of the batteries in these devices. Simple algorithms, though faster and less-power-hungry, are often less accurate in interpreting heart electrical signals, leading devices to overlook some heart conditions, to apply unnecessary electrical therapy, or to apply the wrong type of therapy.
Accordingly, there is a continuing need for algorithms that are not only energy-efficient, but also highly accurate in diagnosing and treating abnormal heart rhythms.